New thread by a relatively new M16 owner.
I’d like to make a modern concept LMG upper without all the internal changes to run open bolt like the Colt LMG. So far I’ve got:
Colt HBAR 20” barrel
Colt BCG and CH
Colt A4 receiver

Any rail, optic, bipod recs?

I’ll be running this mostly suppressed with an AAC M4-2000.

I wonder if an inconel gas tube is worth the cost.  My understanding is the conventional gas tube is usually one of the first parts to melt under long strings of fire.

Running with a suppressor, adjustable gas block to tune gas system, SureFire Optimized Bolt Carrier to reduce rate of fire will also reduce gas blowback somewhat.

Look at a Colt IAR upper.

US Armament used to have them and may still.

It was Colts entry into the modern version of a similar project.

I’m running a Vltor A5 system with an H3. ROF seems controlled enough so far. I’ve seen the IAR. I’m shooting for something that’s basically bipod and flat shooting. I already have a fairly heavy 16” mid length setup that imitates the IAR well enough for me.

That surefire BCG that reduces the rate of rife would be a fun addition. Try and get it down around 600 RPM would give a lot more trigger time

The Surefire BCG is a solid idea. I will likely try a standard M16 carrier (why not?) and if it’s unable to stay on target under some magnification I’ll move to Surefire to slow things down. I have an LMT enhanced BCG to try as well. That may work to slow things down a little too.

The rail is the real question right now. I have a ton of LMT MRPs. I thought about sending the HBAR off to Marvin Pitts and having an MRP upper. I also thought about a Larue rail as I really like their mounts.

I appreciate all the recs.

As a collector, I have no desire to lay on my belly like a reptile. I went the other direction. What wears barrels faster?  Higher temperatures do. So I put a water jacket around the barrel. This upper started out mag fed with five Beta C drums. I had the upper converted to the Valkyrie Armaments belt fed system as I have a DIAS.  The balance is pretty good. Here is my wife shooting a 500 rd burst.

http://m.youtube.com/watch?v=RFcxuOzsoXA

Scott

20” hbar on a mrp would be neat. The AAC m4-2k is a very high back pressure can. I hate mine when compared to other lower back pressure options. You should try a Gemtech suppressed bolt carrier. They work nicely.

I am super interested in this idea. So far I have a 20" HB, regular old flat top upper receiver and I think a melonited gas tube of some sort. I think I got the gas tube on brownells. It is supposed to be more durable. I couldn't really find any other parts that would be useful for a DIY LMG upper. I will definitely be keeping an eye on this thread!

I've done some tinkering with similar configurations....my website is down right now and I just haven't had time to rebuild it all so can't point you guys to some of my pictures/data...

Anyways, I've been playing with my recommended buffer/tube/spring configuration:  hydraulic Kynshot RB5007 / A5 / Tube and 556 Tubb flat spring.
In a Mid gas 5.56 I was getting I think 465 RPM with a FerFrans RRS carrier.

I also have a Surefire SOB that I've had milled out so that it will accept unmodified AK mags/drums for use with my MGI lower and RDIAS.  I have ROF numbers for that but not handy right now.  I know it did drop the rate down and I think that the cam pin geometry of the Surefire BCG should help prevent broken bolts on the 7.62x39.

Also trying the 'PRI Fatboy' gas tube which drops the cyclic rate at least 150 RPM or so if I recall right...gotta check my notes...

They were only made for the carbine gas system...so I'm having some custom rifle and midlength 'fat boy' gas tubes made.

I'm interested to see how the custom fat boy tube system works in a rifle length gas with my preferred buffer/tube/spring and the Surefire SOB and the FerFrans RRS.